threading with live center problem

[jeremyinnys]

i have a hardinge superslant 3 axis lathe. now this job i run used to work but the last couple of years we've had problems. i have to make a part that is 5.5" long with a 5/8-11 thread on the entire length, with a pitch diameter of .55 +,-,.005". i'm centerdrilling the end then my live center just touches until it starts to turn, then moves in .015" more for support. but now it gives me drive faults and blows fuses on that axis drive. must be too much pressure. i really need to use the live center to hold tolerance on that length of part. any suggestions. please and thankx.

[Kool Parts]

jeremyinnys,
Might try puting a indicator in and see if it is really moving .015, or maybe more?
The bearing in the live center would have to really be dragging but maybe switch it out with a diff one?
Gary

[One of Many]

[QUOTE=jeremyinnys] my live center just touches until it starts to turn, then moves in .015" more for support. QUOTE]

Presuming the center bearings are ok. There will be quit a difference in motor loading with less force on the center. If .005-.010 would suffice to keep the drive from faulting, there would be less current required to keep the servo in position. Excess load will eventually lead to a burned commutator also. You might pull one of the brushes and look at the commutator surface for arcing and burns between the poles. Not much you can do about it once it has started. Turning the commutator could save it if it is caught early, but drive problems usually indicate it is more than likely to late.

DC

[jeremyinnys]

hey thanks. i switched to a spring loaded center. we were led to believe the one we had was one too, but it wasn't.

[One of Many]

hey thanks. i switched to a spring loaded center. we were led to believe the one we had was one too, but it wasn't.

Ya know, I almost mentioned a spring loaded center like what Ideal makes, but I let it slide. I don't really trust them much since IMHO, they can ride out of the center drilled hole when under a cutting load if not preloaded properly. A solid center does not present these issues.

DC